This invention concerns an airjet weaving machine with an improved weft thread supply.
It is known that the supply of weft threads on an airjet weaving machine normally consists of several thread preparation mechanisms each made up of at least one thread package, a thread accumulator device such as for example a prewinder, a thread stopping device in order to release suitable lengths of weft thread from the prewinder, and a main nozzle.
Clearly, the various thread preparation mechanisms can work with various types of weft thread, for example in order to weave with several colors.
From Belgian Pat. No. 901.696 it is known to double the number of thread preparation mechanisms. In front of each thread preparation mechanism is placed a thread detector connected to a control unit, such that whenever a broken weft thread is detected in one thread preparation mechanism, the system automatically switches over to the other thread preparation mechanism, enabling weaving to continue without interruption.
The main nozzle of the thread preparation mechanism which is switched off remains in operation, normally at a low flow rate, so that the section of weft thread between the thread stopping device and the main nozzle remains tensioned, otherwise this section of weft thread would fall out of the main nozzle and become entangled in the other weft threads.
When the thread preparation mechanism is switched to standby, the weaver has to intervene in order to repair the defective supply channel. However, it may happen that said section of weft thread has to wait in the main nozzle for too long. The main nozzle is normally mounted on the sley of the weaving machine and so performs a back-and-forth motion, with the result that the section of thread extending into the main nozzle is subject to a heavy load and may break.
If the section of weft thread breaks close to the main nozzle on standby, the piece of thread which comes loose may be blown into the shed along with a weft thread from another main nozzle, so causing a weaving defect which greatly impairs the quality of the woven article.
If said weft thread breaks close to the thread accumulator device, there is a high chance that the piece of thread broken off will become entangled with the other weft threads, in which case either it may be blown along with them into the shed by another main nozzle, or it may block the other main nozzles. In the latter case a weaving machine stop will occur which may last relatively long, since the weaver normally cannot attend to the machine immediately.